Analytical Balance- Definition, Principle, Parts, Types, Examples

An analytical balance is a highly accurate laboratory balance designed to determine an object’s mass precisely. The objects could be solid, liquid, granular substances, or powders. It is also known as laboratory balance which is class II balance.

The balance is extremely sensitive since it provides precise measurement having readability of up to 0.00001 grams (0.01 mg), and is often used in labs. It detects the weight of an object of 100g to within ± 0.01 mg.

Principle of Analytical Balance

Analytical balance calculates weights based on the force required to balance the mass of a sample rather than utilizing actual masses. They produce a force to balance the sample using an electromagnet, then output the result by measuring the force required.  A transparent enclosure with doors surrounds the measurement pan of an analytical balance (0.1 mg or greater), blocking external influences. As a result, dust does not collect, and air currents in the room do not affect the weighing performance.

Parts of Analytical Balance with Functions

• Balance plate (Pan)- A container to bold the sample material for mass measurement.
• Weights- It enables the calibration of analytical scales.
• Power button (on/off button)- It is used to activate or deactivate the balance. 
• ‘Re-zero’ or ‘Tare’ button- It is used to rebalance the system and bring it back to neutral (zero)
• ‘Mode’ button- It is used to configure the measurement conversion system such that the conversion system can be changed as necessary.
• Draft shields- These are incorporated into the design of analytical balances to offer protection from outside factors such as air flows and dust that could compromise precision.
• Level adjustment feet- These enable the balance to be brought to the reference position. These are movable legs. The leveling bubble, spirit level, or plumb bob determines the reference position.
• Level indicator- It checks the balance in level.
• Display panel- It displays various information such as results, errors, information for function settings, and function in progress.

Weighing Procedure of an Analytical Balance

1. Select a proper location

Several external environmental factors influence the measurement. Hence, it’s necessary to carry out the weighing procedures in a suitable location.

1. Choose a stable and horizontal location free from external disturbances.
2. Avoid direct sunlight and make sure there are no extreme temperature changes.
3. Refrain from touching magnetic or magnetic field-generating objects or equipment.
4. The environment should be as dust-free as possible.
5. Steer clear of air currents produced by ventilators, air conditioners, open doors, and windows.

2. Leveling the analytical balance

1. Repeatable measurements and precise findings require precise horizontal positioning.
2. The analytical balance must be leveled to account for any slight deviations or tilts at this site.
3. Until the air bubble in the indicator is in the center, the analytical balance’s leveling feet should be adjusted.

3. Calibrating the analytical balance

1. The analytical balance must be calibrated for the sample to be precisely weighed. The following circumstances call for calibrating the operations:

• Modifications to the usage location (including moving within the same room).
• Alteration in the environment.
• Before each use.

In-built internal calibration or external calibration can be performed. Internal calibration requires manual input from the users to reset the analytical balance, and external calibration is performed using a calibration pendulum.

4. Weighing

1. It is preferable to preheat it for an hour before using it.
2. Set the analytical balance to zero in the no-load condition by pressing the “tare” button.
3. Place the weigh boat, weigh paper, or other vessel or container in the center of the weighing pan and then shut the glass door of the weighing chamber.
4. Check the value that was displayed after it was stabilized. The appearance of the stability mark indicates a stable state.
5. To exclude container mass from the measurement, the ‘TARE’ button is pressed to reset the mass to zero.
6. Add the substance to be weighed after removing the container from the balance. Avoid putting things in the balance pan because doing so can contaminate the balance.
7. Reset the container’s balance, then wait 5-10 seconds (up to a minute) for the mass reading to stabilize.

5. Cleaning

The analytical balance’s measurement accuracy and lifespan are improved by routine cleaning.

1. Use just a piece of lint-free, soap-wet, mild detergent-coated cloth to clean the analytical balance.
2. Avoid using any abrasive or harsh cleaning chemicals as well as organic solvents.
3. Cut off the electricity and unplug the power cord while cleaning.
4. Ensure no liquid or dust gets inside the housing of the analytical balance.

Types of Analytical Balance

1. Two pan or equal arm analytical balance

Joseph Black, a Scottish chemist, introduced two-pan balance. It works on the principle of a first-class lever. The fulcrum serves as a beam over a centered pivot joint to which two pans are attached. Two pans and the central beam are placed in three prism-formed knife edges. Two pans are balanced against each other in which the object to be weighed is placed on one pan while the known weight is placed on the other.

The two sources of error in two pan balance are:

1. The two arms must be equidistant from the center, which is tedious, time-consuming, and difficult in practice. When an arm is only 10^-5 longer than the other arm, it results in an error of 10^-5 of the weight.
2. As the weight increases, the beam may gently flex over the knife edges, causing minuscule measurement inaccuracies. 

2. Single pan or unequal arm mechanical balance

This balance overcomes the limitations of two pan balances. Two knife edges with unequal balance arms are present. The shorter arm supports the balance pan and a full complement of weights, and the longer arm contains a constant counterweight built into the balance beam.

Here, the empty pan is loaded with the object, and weights are removed from the shorter arm to compensate for the weight of the object loaded. Such a type of weighing is known as weighing by substitution.

3. Electronic single pan balance

It is also known as the electromagnetic force balance and has widely replaced the mechanical or single pan balance. The passing current generates a magnetic force that balances the load placed on the balance pan. Thus, the current required is directly proportional to the object’s mass on the pan.

4. Microbalance

It can measure samples to a resolution of at least 1 million parts per gram. To precisely quantify tiny amounts of a sample, microbalances are employed.

Uses/ Applications of Analytical Balance

• Analysis and determination of density
• Preparation of sample
• Pipette calibration
• Differential weighing
• Piece counting
• Interval weighing
• Formulation/ Recipe calculation
• Percent weighing
• Filling
• Gross-net tare weighing
• Checkweighing
• Animal weighing

Factors affecting the performance of an analytical balance

1. Temperature

A slight change in temperature results in a noticeable fluctuation of measurement. An increase in room temperature causes the expansion of the sample or loss of water from the sample, i.e., evaporation. Conversely, lowering the room temperature causes the contraction of the sample or condensation of water vapor.

2. Vibrations

Disturbances from refrigerators, ventilation systems, or other equipment alter the precision of the balance as a result of rearrangement, dislodgement, or spilling of the sample, thereby influencing the amount of material available and its distribution.

3. Chemical Reaction

Highly reactive samples are highly sensitive to atmospheric alterations. Thus, the samples to be weighed should remain chemically inert.

4. Air currents

The sample should be weighed in a well-ventilated room to ensure precise measurement and safety of lab workers as violent air currents result in a change in air pressure and hence, a misalignment in the sensitive support.

5. Calibration

An accurate reading by an analytical balance is provided when the instrument is calibrated. Some of these instruments have in-built internal calibration features that conduct calibration tests themselves with minimal contribution from the user. However, some require certified calibration masses and external effort from the user to determine calibration settings based on the specific lab environment.

6. Magnet

Inaccurate reading during sample weighing could be attributed to the nature of the samples. If the sample is magnetic or is magnetized, it may attract other elements or create a magnetic field that influences the sensor coil of the balance.

7. Fingerprints

If the sample size is very small (approximately 0.1 mg), fingerprints may alter the results.

Advantages of Analytical Balance

• A very high degree of accuracy
• It is simple, useful, quick, and efficient to determine an object’s mass.
• The self-calibration system permits a weight adjustment mechanism and ensures that the scale is always correctly set and produces the most precise results.
• These balances can detect the smallest weight variations to the nearest decimal point.
• It assists laboratories in upholding and enhancing acceptable good laboratory practices (GLPs).
• The measurement through analytical balance ensures uniformity, consistency, reliability, quality, reproducibility, and integrity.

Limitations of Analytical Balance

• The accuracy and precision of the balance rely on environmental factors where the weighing is performed. Thus, fluctuation in readings can be seen.
• It’s not intended for use in rigorous measurements.
• Care must be taken with a very delicate weighing device.
• LCDs can be easily damaged due to heavy loads.
• Heavy loads have the potential to harm LCDs easily.

Precautions

• The balance should be kept calibrated. The standard weights should not be touched with hands.
• The weighing process should be done in an appropriate environment free of vibrations and under controlled humidity and temperature. Avoid direct exposure to sunlight and place the balance away from the area of excessive air drafts while weighing.

Analytical Balance Examples and Products

a. Analytical laboratory balance XPR (Manufacturer: Mettler Toledo) 

Features

• With the XPR Automatic Balance, you may attain a degree of weighing accuracy unequaled by human methods. 
• At 2 g readability, incredibly tiny sample quantities can be dispensed, ensuring that expensive and uncommon materials are used sparingly. 
• Because external sources of error have a minimal impact on the weighing process, the automated approach is time-efficient and produces highly reproducible findings.
• Built-in sensors enable you to dispense into even the smallest tare containers, eliminating sample transfer and related mistakes.

b. BA-B Series Electronic Analytical Balance (Manufacturer: Biobase)

Features

• Innovative design, a five-sided, fully transparent windscreen, and a humanized design. High precision is ensured using an electromagnetic balance weighing sensor of the latest generation.
• Application programs such as four-point linear calibration, automatic fault detection, and over-load protection
• A sharper and more comfortable visual experience is provided when using an ultra-large LCD.

c. Analytical laboratory balance AS 62/220.R2 (Manufacturer: Radwag Balances and Sales)

Features

• 60 / 220 g Maximum capacity

• 0.01 / 0.1mg Readability
• The AS R2 PLUS stands out thanks to various contemporary constructional and system solutions that ensure reliability, precision, and measurement accuracy and simplify daily use.
• The roomy weighing chamber of the most recent AS R2 PLUS analytical balance and the open-door clearance allow simple access to the weighing pan.
• Innovative building techniques boost a balance’s long-term dependability and longevity.
• Level control is made easier by the leveling mechanism installed in front of the weighing chamber on standard AS R2 PLUS balances.

d. Analytical laboratory balance 390 (Manufacturer: Precisa Gravimetric AG)

Features

• High-end weighing cell: Optimised electrical control and high resolution
• Housing: A strong sheet metal housing with a die-cast aluminum base.
• 7″ anti-reflective, high-resolution touch screen. UV resistant, authorized for use with common laboratory gloves, shock and scratch resistant, and frameless for ideal and simple cleaning
• Context Help: Simply click the Help icon, and the balance will display any pertinent support or assistance in the current context
• Draft shield: Mechanically operated with either hand, electronically with a fingertip, or even automatically using a special touch-free sensor from Precisa (TLS)
• System for internal self-linearization and calibration that is fully automatic, programmable, and temperature-controlled (SLS)

References

1. https://www.precisa.com/blog/what-is-an-analytical-balance/
2. https://www.slideshare.net/orpillalester/the-analytical-balance
3. https://ussolid.com/blog/how-to-properly-use-an-analytical-balance/
4. https://hyprowira.com/en/blog/analytical-balance-sections
5. https://www.grainger.com/know-how/equipment-information/kh-laboratory-balance-scale-types-care-terms
6. https://owlcation.com/stem/A-Quick-Look-at-Mass-Volume-and-Density
7. https://www.labmanager.com/laboratory-technology/analytical-balances-and-proper-weighing-practices-1805
8. https://www.medicalexpo.com/prod/mettler-toledo/product-74754-613073.html
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10. https://www.medicalexpo.com/prod/radwag-balances-scales/product-112787-755574.html
11. https://www.medicalexpo.com/prod/biobase/product-84845-777138.html